Galileo and
Einstein: Using History to Teach Basic Physics to Nonscientists

Galileo and Einstein is an introductory physics
course designed for first year nonscientists given each Spring at the
University of Virginia with an average enrollment of just over a hundred
students.

About ten years ago, the University of Virginia began
encouraging faculty to give University Seminars, which could be rather informal
one-semester two credit hours minicourses, intended mainly for first year
students, with a maximum enrollment of twenty. I had been reading and enjoying Galileo's Two New Sciences at the
time, and it occurred to me that this text could perhaps be the basis of a
University Seminar for nonscience students. The book covers a wide variety of topics. Admittedly, some sections are hopelessly obscure, but then whole
stretches of the book are beautifully written and very illuminating. For example, Galileo gives a clear analysis
of why there can be no giants, and the arguments he presents are as relevant as
ever—easily applied to demolish many Hollywood fantasies, from giant ants to
shrunken kids. His discussion of
falling motion is of course a classic: why Aristotle had to be wrong, and, more
practically, how to figure out the range of a cannon. When I began to put the Seminar together, I decided to add some
selections from The Starry Messenger: Galileo's memorable description of
his discovery of the Moons of Jupiter, the phases of Venus, and mountains on
the Moon, and how well it all fitted into Copernicus' scheme.

I used these books for the Seminar because they were
written almost four hundred years ago. Their insights and conclusions followed from simple observation and
careful reasoning, not dependent on the abstractions and subtleties of modern
science. Even calculus hadn't been
invented when they were written. Galileo
aimed for a wide audience, and wrote in a breezy style (I used the Crew translation,
more accessible than Drake). I felt
that once our students got used to the approach, they would be able to follow
the arguments pretty well.

As I soon discovered, though, Galileo's audience knew a lot
more than our students. He assumed some
knowledge of elementary Greek geometry, and of Greek astronomy. I found my students knew almost no geometry,
and many of them did not understand, for example, why there are seasons. I was
obliged to back up and give some introductory lectures on Greek geometry and
astronomy. These proved very
enlightening for the students. They
were amazed to discover that the Greeks had a fairly accurate measure of the
size of the earth—they thought that before Columbus, no one really believed the
earth was round. They were dumbfounded
that the Greeks had measured the distance to the Moon, and got it close to
right.

To give the students some insight into how the Greeks
reached all these remarkable conclusions, I had to get them thinking
geometrically, at least in a semiquantitative fashion. I began by giving out practical homeworks,
which they did in pairs. We began with
some very simple surveying around the University Grounds, estimating the
heights of buildings by pacing out distances on the ground, measuring an angle,
then doing a scale drawing (no calculation, and certainly no
trigonometry). Then they measured the
angle of the Pole Star and another star, and found on returning a couple of
hours later that the Pole Star hadn't moved, the other star had. We built up a picture of how the stars move
through the sky, and how that movement would be perceived at different places,
for example at the North Pole or at Quito, on the equator. We next discussed sundials at different
places on earth, and why clocks go clockwise. I used a white styrofoam ball illuminated by a spotlight, against a
black background, to illustrate phases of the Moon. By putting a small video
camera on the surface of a globe (the Earth) and using it to "observe the Moon"
(the styrofoam ball) it was possible to show how the crescent Moon appears at
different angles to the horizon when observed from different places on Earth
(the video camera was small enough to move around on the globe). The aim of course was for them to build a
clear three-dimensional picture of the earth-moon-sun system, a necessary
preparation for understanding just how the Greeks figured out the distance to
the Moon by watching eclipses and drawing diagrams. This minireview of Greek science proved to be an effective
preparation for Galileo.

Along with reading Two New Sciences, we did some of
the experiments. We rolled a ball down
a ramp, and timed it with a water clock. This was done by a group of students, who did indeed discover that the
ball rolled four times as far in twice the time (contrary to their
expectations!) Perhaps it's worth
noting here that whenever we did any kind of demonstration or experiment, I
asked the students to think first what they expected to see. For the ramp, I
would ask the class to predict how far the ball would roll in twice the time,
and have them write down their prediction. I gave them two or three minutes to do that. Then I asked them to consult with their neighbor and try to reach
a consensus. Finally, they got together
in groups of four. I would pick a group at random, ask them what they
predicted, and invite comment where appropriate. After some discussion, we rolled the ball down the ramp to find
out if they were right. Finally, I
presented Galileo's argument as to why the ramp motion should be a good
representation of falling motion, and mentioned its shortcomings as a way to
measure acceleration of a falling body.

Next, we did an experiment Galileo would have liked to have
done—dropping a ball in front of a measuring stick, making a video, and playing
it back frame by frame to see how far the ball falls between successive frames.
We spent a great deal of time (as did Galileo) analyzing the distances fallen
in successive time intervals, and verified Galileo's prediction that the intervals
go as the odd integers. We plotted graphs and defined acceleration. I found it
was also well worth doing the slightly more tricky experiment of videoing a
ball thrown directly upwards, and having the students plot the position,
average velocity and acceleration at a sequence of points including the
turnaround, because, despite everything taught so far, they still confuse
acceleration and velocity, and will tell you there is zero acceleration at the
topmost point. (This is a good question
to ask them in class, and have them consult with neighbors, etc.) Another neat video experiment we did was to
project a ball horizontally, and discover from the video that the
vertical motion was the same as for a falling ball, but the horizontal motion
was at uniform speed. This is of course a direct representation of the famous "Compound Motion" Galileo used to
find the range of a cannon as a function of muzzle speed and angle of
projection, and his diagram from Two New Sciences can be placed next to
the video. It's an excellent match.

Having worked so hard to understand acceleration in
projectile motion, I couldn't resist taking the next step, beyond Galileo. It takes very little work at this point to
extend the analysis, following Newton, to a projectile fired from a high
mountain, a cannonball moving so fast that the earth's curvature must be taken
into account. This was the crucial step
that Galileo missed: it unifies the familiar motion of a thrown stone with the
celestial motion of the moon. From there
to the planets and Universal Gravitation is straightforward. I later made an applet of Newton's cannon on
a mountain, with the help of a graduate student programmer. It brings the
famous image in the Principia to life. You can easily find it on the
web by googling Newton
mountain.

After teaching the seminar this way in my first year, I
decided to drop some of the more obscure sections of Two New Sciences I
had been covering, and instead to give lectures on Kepler and Brahe. These proved popular, and at that point I
felt I had a complete course, beginning with Thales and Pythagoras, and ending
with Newton's laws and Universal Gravitation. In fact, as must be evident from the above, I found in practice that
working through Galileo's arguments in Two New Sciences was an excellent
preparation for Newton's Laws. Galileo
already states the First Law, in essence, and the sticking point in the Second
Law is understanding the very difficult concept of acceleration. Galileo's
thorough discussion of one-dimensional acceleration, and his "Compound Motion"
generalization to parabolic motion in two dimensions, leads naturally via the
Newton Mountain example to circular motion. Following this trail makes it much more plausible that steady circular
motion means acceleration towards the center. (It is also helpful to rediscuss parabolic motion, taking the example of
a cannonball projected upwards at an angle, and think about the acceleration at
the topmost point, comparing that with circular motion). To round out the discussion, this is an
appropriate place to introduce the idea of velocity as a vector
(admittedly a postNewtonian concept) and acceleration as the rate of change of
that vector quantity.

It is perhaps not evident from the above that I used
countless demonstrations, most of them involving the students, to illustrate
these concepts. I tried to stay away from fancy equipment. For example, in discussing the Second Law, to
convince them that a centripetal force was necessary for circular motion,
students attempted to make a bowling ball go in a circular path on a smooth
floor by guiding it with a broom. They almost always tried by pushing it from
behind, reminiscent of Kepler's theory of planetary motion, and of course
classically Aristotelian. However, they quickly discovered that they really did
have to push the ball "sideways" to get circular motion. We tested the Third Law by having students
of very different masses collide in carts, using old kitchen spring scales to
bounce off each other and at the same time measure the force felt be each. Another "weighing" experiment illustrated
Galileo's assertion that one does not feel the weight of a load on one's
shoulder if one is falling (incidentally, a precursor of Einstein's "happiest
thought" that led to General Relativity). I had the students weigh themselves on a spring scale in an elevator,
and to note how their weight varied as the elevator started and stopped.

The problem with the course as described above was that
although it received very positive student evaluations, and I believe gave them
some sense of Newtonian mechanics and how the ideas evolved historically, it
did not attract enough nonscience majors, at least in the eyes of the
administration. This is why I brought
in Einstein. I don't feel too
apologetic, in many ways it was a natural extension of the course—Newton was
the first major revolution in Physics, and Einstein the second. Furthermore, it made evident the limits of
validity of Newton's Laws. And,
actually, it is easier for students to grasp the essential points of Special
Relativity that it is for them to understand Newton's Laws, at least in my
experience.

So devoting the last third of the course to Einstein has led
to a much more popular course, with over a hundred students enrolled. This has necessitated cutting out some of
the earlier historical material, but there is still time for a reasonably
thorough coverage of many of Galileo's arguments, and of Newton's Laws.

All the course materials are readily available on the web,
including full lecture notes. My
website was visited 375,000 times in the year 2000. To visit, just google Galileo Einstein.

The
Basic Books

Galileo Galilei, Dialogues
Concerning Two New Sciences. Translated by Henry Crew and Alfonso de Salvio, Dover NY, 1954 but still
in print. ISBN 0-486-60099-8.